Buddy of mine bought a 1986 Catalina 30 in 2005 with literally hundreds of blisters on it. We (he and I) spent 3 weekends grinding, filling and fairing, then barrier coated and bottom painted. We did not strip all gell coat, we spot repaired each one, merging several when needed and used a long stip of flexible wood as a fairing batten.
Total cost - 600 - 700 bucks and 3 weekends of going home covered in blue dust. I already had two angle grinders and large sanders - blew my shopvac to hell so my buddy replaced it. I did some gelcoat fixes during that time period while he was pasting in epoxy (no dust periods).
The original asking price was 24k, he paid 16k. The owner was 70+ and needed to dump the boat, it had not left the pier in 3 years.